Progress in computational sciences and acoustic field theory has opened interesting possibilities in sound technology. As a practical example of new technologies, a tool relatively new on the market is a software product that can be used to create an impression of position of a source of an audio signal when a user listens a representation of the audio signal through at least two channel headphones.
In practice, when such a tool is run in a processor in a form of a software product, the audio signal will be passed through a head-related transfer function (HRTF) in order to generate, for a user wearing at least two channel (e.g. stereo) headphones, a psychoacoustic impression of the audio signal arriving from a predefined position.
The mechanism how the psychoacoustic impression is created can be illustrated by way of an example. As we know from the daily life, a person can observe the position r (bold denotes here a vector which may be expressed with r, Φ, and θ in spherical coordinates) of a sound source with a rather good precision. So if sound is emitted by a sound source located close to the left ear (r=30 cm, Φ=3 π/2, θ=0), it is first received by the left ear and only a fraction of a second later by the right ear. Now if an audio signal is reproduced through headphones first to the left ear and the fraction of a second later by the right ear through headphones, which can be performed by filtering the signal through a respective head-related transfer function, the listener gets an impression of the sound source being located close to the left ear.
A more thorough discussion of different properties of a HRTF and how it can be obtained can be found e.g. in published US patent application 2004/0136538 A1, which is incorporated by reference in its entirety herein.
Additional features and advantages of the present invention are described in, and will be apparent from, the following Detailed Description of the Invention and the figures.